Method for preparing polar thermoplastic resin compositions having improved gas barrier properties

Abstract

A method of preparing a polar thermoplastic resin having improved resistance to gas permeability is disclosed wherein a blend of the resin and coarse mica flakes having an average particle size of less than about 100 mesh is prepared, the blend being prepared under mixing conditions which impart a shear force to the mica flakes sufficient to delaminate the flakes into individual platelets, substantially increasing the original aspect ratio of the flakes whereby an increase in the gas barrier properties of the resin is attained greater than that attained with fine mica flakes having an average particle size greater than about 100 mesh.

What is claimed is: 
     
       1. A method of preparing a polar thermoplastic resin having increased resistance to gas permeability which comprises providing a blend of the resin and mica flakes having a plurality of platelets, the flakes having a particle size less than about 100 mesh before blending and then admixing the mica flakes and resin at a temperature at which the resin is molten, the admixing imparting a shear force which effects delamination of the mica platelets and a substantial increase in the aspect ratio whereby improved gas barrier and heat stability properties are achieved. 
     
     
       2. The method of claim 1 wherein the polar thermoplastic resin is a polyalkylene terephthalate. 
     
     
       3. The method of claim 2 wherein the polyalkylene terephthalate is polyethylene terephthalate. 
     
     
       4. The method of claim 1 wherein the average particle size of the mica flakes blended with the polyalkylene terephthalate is about 10 to about 100 mesh. 
     
     
       5. The method of claim 1 wherein the aspect ratio of the mica flakes before blending is less than about 40. 
     
     
       6. The method of claim 1 wherein the blend mixture is comprised of about 20 to about 80 percent by weight of the polar thermoplastic resin and about 20 to about 80 percent by weight of the mica flakes. 
     
     
       7. The method of claim 6 wherein a polyepoxide is added to the blend at a concentration of from about 0.1 to about 10 percent by weight. 
     
     
       8. The method of claim 7 wherein the polyepoxide is the condensate of Bisphenol A and epichlorohydrin. 
     
     
       9. The method of claim 1 wherein the admixing is performed at a temperature of about 200° C. to about 350° C. 
     
     
       10. The composition comprised of a blend of a polar polymer and mica prepared by the method of claim 1. 
     
     
       11. The composition of claim 10 wherein the polar thermoplastic resin is a polyalkylene terephthalate. 
     
     
       12. The composition of claim 11 wherein the polyalkylene terephthalate is polyethylene terephthalate. 
     
     
       13. The composition of claim 10 wherein the blend mixture is comprised of about 20 to about 80 percent by weight of the polar thermoplastic resin and about 20 to about 80 percent by weight of the mica flakes. 
     
     
       14. The composition of claim 13 wherein a polyepoxide is added to the blend at a concentration of from about 0.1 to about 10 percent by weight. 
     
     
       15. The composition of 14 wherein the polyepoxide is the condensate of Bisphenol A and epichlorohydrin. 
     
     
       16. A method of forming a thermoplastic container having increased gas barrier and heat stability properties and adapted to be used for the packaging of foodstuffs highly susceptible to oxidative deterioration which comprises providing a blend of a polar thermoplastic resin and mica flakes having a plurality of platelets, the flakes having an average particle size less than about 100 mesh, admixing the mica flakes and polar thermoplastic resin at a temperature at which the resin is molten, the admixing imparting a shear force which effects delamination of the mica platelets to effect a substantial increase in the aspect ratio of the flakes with a concommitant increase in the gas barrier properties of the resin, and then molding the admixture into a container. 
     
     
       17. The method of claim 16 wherein the resin is a polyalkylene terephthalate. 
     
     
       18. The method of claim 17 wherein the polyalkylene terephthalate resin is polyethylene terephthalate. 
     
     
       19. The method of claim 16 wherein the aspect ratio of the mica flakes blended with the polyalkylene terephthalate has an aspect ratio of less than about 40. 
     
     
       20. The method of claim 16 wherein the blend mixture is comprised of about 20 to about 80 percent by weight of the polyalkylene terephthalate resin and about 15 to about 75 percent by weight of the mica flakes and about 0.5 to about 10 percent by weight of an epoxy resin. 
     
     
       21. The method of claim 16 wherein the mica flakes added to the blend have a particle size ranging from about 10 to about 60 mesh. 
     
     
       22. The method of claim 16 wherein the admixing is performed at a temperature of about 200° C. to about 300° C. 
     
     
       23. The method of claim 16 wherein the admixture is molded into a container by compression molding. 
     
     
       24. The method of claim 16 wherein the admixture is molded into a container by injection molding. 
     
     
       25. The method of claim 16 wherein the admixture is molded into a container by thermoforming. 
     
     
       26. A container manufactured by the method of claim 16. 
     
     
       27. A container manufactured by the method of claim 20.